1. Technical Field
This application relates to UMTS (Universal Mobile Telecommunications System) in general, and to an apparatus and method for handling messages that relate to a cell other than the currently operating cell in universal mobile telecommunications system user equipment in particular.
2. Description of the Related Art
In a typical cellular radio system, mobile user equipment (UE) communicates via a radio access radio network (RAN) to one or more core networks. User equipment (UE) comprises various types of equipment such as mobile telephones (also known as cellular or cell phones), lap tops with wireless communication capability, personal digital assistants (PDAs) etc. These may be portable, hand held, pocket sized, installed in a vehicle etc and communicate voice and/or data signals with the radio access network.
The radio access network covers a geographical area divided into a plurality of cell areas. Each cell area is served by at least one base station, which may be referred to as a Node B. Each cell is identified by a unique identifier which is broadcast in the cell. The base stations communicate at radio frequencies over an air interface with the UEs within range of the base station. Several base stations may be connected to a radio network controller (RNC) which controls various activities of the base stations. The radio network controllers are typically connected to a core network.
UMTS is a third generation public land mobile telecommunication system. Various standardization bodies are known to publish and set standards for UMTS, each in their respective areas of competence. For instance, the 3GPP (Third Generation Partnership Project) has been known to publish and set standards for GSM (Global System for Mobile Communications) based UMTS, and the 3GPP2 (Third Generation Partnership Project 2) has been known to publish and set standards for CDMA (Code Division Multiple Access) based UMTS. Within the scope of a particular standardization body, specific partners publish and set standards in their respective areas.
Consider a wireless mobile device, generally referred to as user equipment (UE), that complies with the 3GPP specifications for the UMTS protocol. The 3GPP 25.331 specification, v.3.15.0, referred to herein as the 25.331 specification, addresses the subject of UMTS RRC (Radio Resource Control) protocol requirements between the UMTS Terrestrial Radio Access Network (UTRAN) and the UE.
In accordance with (clause 8.2.2.3 of) the 25.331 specification, the UTRAN may send a message to the UE which includes an information element (IE) known as C-RNTI (Cell-Radio Network Temporary Identifier). The value of C-RNTI is unique within a given cell; but values may be re-used in neighbouring cells. The message can be acted on immediately or at some time in the future, generally up to a maximum of 2.55 seconds in the future, although usually this is expected to be considerably less than that. The UE may reply with a response message, which would normally be sent from the UE at or shortly after the UE has acted on the received message.
When switching from a dedicated to a common channel in UMTS, the UE is assigned a temporary identifier known as C-RNTI (Cell Radio Network Temporary Identifier). This temporary identifier C-RNTI is specific to a cell and is valid in the cell where the UE uses resources. The C-RNTI is used to distinguish between different user equipment in that cell.
An example of such a procedure is illustrated in FIG. 1, in which a Reconfiguration command is sent at S10 from the UTRAN to the UE, with a new configuration X. The requested new configuration X, typically a dedicated physical channel, is applied at both the UE and the UTRAN at an activation time. The new configuration is received by the UE at S11 is generally applied at the UE before sending a Reconfiguration_COMPLETE response at S12. If the reconfiguration fails for any reason, the UE will revert to its previous configuration and may send a Reconfiguration_FAILURE message indicating that the reconfiguration has failed.
However, if an event occurs that requires a cell update to be invoked while the reconfiguration procedure is ongoing, the current 3GPP standards do not unambiguously define the required behaviour of the UE, so potentially leading to interoperability problems. Some examples of events requiring a cell update to be invoked are defined in clause 8.3.1.2 of the 25.331 specification and include the conditions of radio link failure, re-entering service area, RLC unrecoverable error, cell re-selection and periodical cell update.
A typical cell update procedure is illustrated in FIG. 2. On the occurrence of a trigger event at S20, the UE selects a new cell (cell 2) and moves to communicate with cell 2 at a time indicated by the dotted line. The UE then sends a CELL UPDATE request message to the UTRAN at S22, which tracks the state of the UE. The UTRAN returns a CELL UPDATE CONFIRM (Y) message, where Y represents the reconfiguration carried by the CELL UPDATE CONFIRM message. Both the UTRAN and UE apply the new configuration Y and the UE sends a response to the UTRAN, confirming the completion of the reconfiguration procedure. When the procedure completes, the UTRAN knows both the state of the UE and its current configuration (FACH+Y), as required to maintain communication.
In addition to the general interaction of the cell update and reconfiguration procedures, another scenario needs to be taken into account when designing UTRAN behaviour. This is the crossover of the CELL UPDATE command with the Reconfiguration command.
FIG. 3 illustrates the situation where a Reconfiguration command is issued by the UTRAN at S30 but reaches the UE at S33 after the UE has undergone a trigger event at S31 which causes the UE to move to cell 2 and to send the CELL UPDATE command to the UTRAN at S32. In this case, since CU has started, the Reconfiguration command is rejected per clause 8.6.3.11 of the 25.331 specification. The UE and UTRAN then apply the cell update configuration Y at S34 and S35. The UE then sends a confirmatory response message at S36 and a Reconfiguration_FAILURE message at S37 to the UTRAN. If the UTRAN applies X on receipt of the cell update response message, it must revert to the previous configuration when it receives the Reconfiguration_FAILURE message.
There are thus proposed strategies for dealing with messages that may contain a C-RNTI that relates to a cell other than the cell in which the UE is currently operating. A number of such strategies are detailed below.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of an apparatus and method for handling messages that relate to a cell other than the currently operating cell in a UMTS user equipment.
The same reference numerals are used in different figures to denote similar elements.